The purpose of this project is to examine genetic factors in rats that control immune responses and susceptibility to tumors induced by oncornaviruses. Humoral and cellular responses to viral and to other antigens will be measured by radioimmunoassays. These studies will include the amount and immunoglobulin class of antibodies and the amount and type of immune cells. Measurements will be made both during tumor growth and following immunization with virus or viral polypeptides. Genetic controls of responses will be related to the major histocompatibility (RT1) locus and to other phenotypic traits. Whether the quantity of virus released by tumor cells or the levels of virus replication differ in susceptible and resistant strains will also be examined. We plan to identify and amplify mechanisms of tumor resistance.